1. Field of the Invention
The present invention relates to a wafer inspection system and a method thereof, and more particularly, to a wafer inspection system and a method thereof, in which a wafer defect is sorted by an in-line method.
2. Description of the Related Art
After a semiconductor chip (hereinafter, referred to as “die”) is completed on a wafer through deposition, photolithography, etching, ion implantation, etc., an EDS (electrical die sorting) process is performed to test electrical performance of each die.
The EDS process includes a burn-in process to test the durability of the die, a pre-laser process applying an electrical current to the die to check a defective die according to operation states, and a laser repair process to scan and repair the defective die with a laser, etc.
In the pre-laser process of the EDS process, the electrical current is applied to the die by controlling a probe to be in contact with a pad of the die, thereby checking an operating state of the die. If the probe abnormally contacts the pad, a boundary line of the pad may be damaged, and an effective electrical test may not be expected. Hence, it is important to control the probe to come in contact with a center of the pad.
The wafer passing the electrical test is loaded on a defect inspection apparatus, which detects a defect in the loaded wafer and stores a position of the defect in the loaded wafer. The stored defect position is used in the following process of detecting a kind and a degree of the defect in each die. It is determined whether the die is a defective or not according to kinds and degrees of the detected defect.
However, in a conventional system for inspecting the wafer, an inspector subjectively determines the kinds and the degrees of the defect in the wafer through an electron microscope. Therefore, it is difficult to apply the same objective standard to all wafers because the defect is subjectively determined. Further, it takes too much time and effort to train an inspector to obtain a reliable inspection result.
There is a conventional inspection apparatus that samples the wafer during a fabricating procedure of the wafer and analyzes the kinds and causes of the defect in the sample wafer. However, this conventional inspection apparatus just uses a feedback from the analysis in the above process, but the feedback cannot be used in instantly determining whether the sample wafer is a defective or not. Further, this conventional inspection apparatus determines the kinds of the defect in the wafer by storing a partial image of a normal wafer as a reference image and comparing the reference image with a defect image of the sample wafer. Therefore, a position of the wafer must be correctly adjusted when the defect image of the sample wafer is photographed. Further, after a final fabricating procedure, a background image for the die and a circumference of the pad is very complicated, so that it is difficult to get correct information about the defect in the wafer by comparing the reference image with the defect image of the sample wafer.